[Qemu-devel] KVM call minutes for Mar 30

[Chris Wright]

vhost-blk
- started w/ vhost-net, nice and modular
- qemu merging requests, so outperforming (throughput) for sequential write
- random read/write and sequential reads are comparable or better
- can't do e.g. qcow2
- spreading work across all cpu workqueues
- are there cases where we expect vhost-blk is needed?
  - not driven by poor perf benchmarks, more driven from interest/curiosity
  - hch's numbers (esp. large request) are solid
  - low hanging fruit...no interrupt mitigation, addr lookup on all request
  - get some performance numbers and profiles to see what we can do to
    improve existing virtio before moving to vhost

qemu optimizations (re: above addr lookup)
- no long lived ptr to guest memory
- ram memory patch allowed for stable mapping
  - objection was memory hotplug/remove
    - how much do we want to gate qemu progress on memory hotplug?
- http://wiki.qemu.org/Features/RamAPI

ide emulation
- qemu virtio-blk vs. other hv ide emulation...ide was better
  - this was some time ago
  - older qemu, even qemu ide emulation was better than virtio-blk in
    some cases
- ide still bounce buffering, and has some fundamental limitations
  (some of those may be fixable w/ ahci)
- anyone looked at this recently?